The present invention relates to an ultrasound assisted process for increasing the crystallinity and crystallization rate of slow crystallizable polymers. More particularly, the present invention relates to a process wherein slow crystallizable polymer melts are subjected to ultrasound treatment, in a pressurized treatment zone, to bring about an increased rate of crystallization. Slow crystallizable polymers, such as polyesters, are of particular interest.
The conversion of a crystallizable polymer from the amorphous to crystalline state is generally achieved simply through cooling of the crystallizable polymer. Increasing the rate of crystallization or the level of crystallinity can also be achieved by stretching of the crystallizable polymer, under certain temperature conditions. This method, however, involves apparatus for stretching and heating, and may only be used when producing certain products, such as, for example, spun fibers or drawn films.
There exist a need in the art for a process to increase the crystallinity of a crystallizable polymer during other processes, such as blow molding, injection molding, and extrusion. The process of the present invention serves to provide a means for increasing the crystallinity or rate of crystallization of crystallizable polymers, particularly xe2x80x9cslowxe2x80x9d crystallizable polymers, in processes not limited to those involving stretching and heating, and will include processes such as blow molding, injection molding and extrusion.
Herein, xe2x80x9cslow crystallizable polymersxe2x80x9d are to be considered those crystallizable polymers that exhibit crystallization rates lower than that of polyolefins, such as polyethylene and polypropylenes. By way of non-limiting example, slow crystallizable polymers include certain types of polyesters, polyimides and polyethers. Given the criteria above, xe2x80x9cslow crystallizable polymersxe2x80x9d will be readily identifiable by those of skill in the art.
Polyesters are of particular interest in the present invention. Polyesters are widely used to manufacture fibers, films, bottles, and other various molded extruded, and spun products, and are known to be slow crystallizable polymers. The ability to control their crystallinity during processing methods, such as molding, extrusion, and fiber spinning, would allow for the manufacture of products having desirable properties. Thus, in a particular embodiment, the present invention proposes an ultrasonic assisted process for making novel polyester resins and products thereof having controlled crystallinity.
In general, the present invention provides a process for increasing the crystallinity of a slow crystallizable polymer. In this process, at least one slow crystallizable polymer is introduced to a pressurized treatment zone along a flow direction, and is subjected, at the pressurized treatment zone, to longitudinal vibrations of ultrasonic waves. In a particularly preferred process, the ultrasonic waves propagate in a direction perpendicular to the flow direction of the at least one slow crystallizable polymer.
The process herein is practiced as a continuous process, and, after ultrasonic treatment in the pressurized treatment zone, the at least one slow crystallizable polymer may be advanced to typical molding, extruding, fiber spinning or other apparatus. Thus, the crystallinity of the at least one slow crystallizable polymer may be controlled during processes for manufacturing useful products from such polymers.
Without wishing to be bound to any particular theory, the increased crystallinity of the slow crystallizable polymers subjected to the present process is believed to be due to a rearrangement and change of mobility of the crystallizable entities in the at least one slow crystallizable polymer that is brought about by the application of the ultrasonic waves. For a given crystallizable polymer or mixture of multiple crystallizable polymers, it may be possible to prepare polymer resins of controlled crystallinity suitable to manufacture products having desirable properties.
As a product of the present process, this invention provides a crystallized polymer prepared by the process for increasing the crystallinity of a crystallizable polymer comprising the steps of introducing at least one slow crystalizable polymer to a pressurized treatment zone and subjecting the at least one crystallizable polymer, at the pressurized treatment zone, to longitudinal vibrations of ultrasonic waves. These crystallizable polymer products are preferably introduced to the pressurized zone along a flow direction that is perpendicular to the direction in which the ultrasonic waves propagate.